1. Field of the Invention
The present invention relates to a double cross type seal device for reducing air leakage through seal plates between mutually adjacent inner shrouds of gas turbine stationary blades.
2. Description of the Prior Art
FIG. 4 is a cross sectional view showing a prior art fitting state of seal plates between gas turbine stationary blade inner shrouds which are mutually adjacent in a turbine circumferential direction and FIG. 5 is a cross sectional view taken on line B--B of FIG. 4. In FIGS. 4 and 5, numeral 11 designates a stationary blade and numeral 12 designates an inner shroud thereof. Numeral 31 designates a moving blade, which is adjacent to the stationary blade 11 in a turbine axial direction, and numeral 32 designates a platform of the moving blade 31. Numeral 13 designates a seal ring support ring provided in the inner shroud 12 and numeral 14 designates a labyrinth seal, which is supported by the seal ring support ring 13 to provide a seal for rotating portions. Numerals 15, 16 designate seals provided respectively at both end portions in the turbine axial direction of the inner shroud 12, said seals constructing seal portions of seal air for platform end portions of adjacent front and rear moving blades.
Numeral 17 designates a seal plate, which is fitted with its side end portion being inserted into a groove 21 provided along the turbine axial direction in the inner shroud 12. Numerals 18, 19 designate also seal plates, which are disposed respectively in side end portions of front and rear flanges of the inner shroud 12 so as to be substantially orthogonal to the seal plate 17 and are fitted with their respective side end portions inserted into grooves 22, 23 provided in the side end portions of the flanges.
These seal plates 17, 18 and 19, as shown in FIG. 5, are fitted with their respective side end portions inserted into the grooves provided in the stationary blade inner shrouds 12, 12' which are mutually adjacent in the turbine circumferential direction, wherein the seal plate 17 is inserted between the grooves 21, 21', the seal plate 18 is inserted between the grooves 22, 22' and the seal plate 19 is inserted between the grooves 23 (FIG. 4), thereby a seal portion is constructed so as to surround a cavity 24.
In the construction of seal plates as mentioned above, seal air 20 is supplied into the cavity 24 from a seal air supply pipe provided in an interior of the stationary blade 11 partly to pass through a hole 25 provided at a front portion of the seal ring support ring 13 and then like arrows 20a, 20b through a space between a mutually adjacent stationary blade and moving blade and to flow out of a seal 15 like arrow 20c. Also, the seal air 20 partly passes through a hole 26 provided at a rear portion of the seal ring support ring 13 and then like arrows 20d and 20e through a space between a mutually adjacent stationary blade and moving blade and to flow out of a seal 16.
While an interior of the cavity 24 is thus maintained by the seal air 20 at a higher pressure than in an outside combustion gas passage so that a high temperature outside combustion gas is prevented from coming in there, the seal air 20 in the cavity 24 leaks from a gap of a joint portion of the seal plate 17 and the seal plate 18, like arrow 20f, and from a gap between an inner end portion of the seal plate 18 and the seal ring support ring 13, like arrow 20g. Likewise, the seal air 20 leaks from a gap between the seal plate 17 and the seal plate 19, like arrow 20h, and from a gap between an inner end portion of the seal plate 19 and the seal ring support ring 13, like arrow 20i. Thus, not a small amount of the seal air 20 leaks from gaps of the seal plates 17, 18 and 19 resulting in a lowering of the sealing ability.
In the prior art construction of the gas turbine stationary blade seal plates as mentioned above, there are two places of air leaking gaps between the seal plate 17 and the seal plates 18, 19 and also two places of air leaking gaps between the inner end portions of the seal plates 18, 19 and the seal ring support ring 13 and this leakage of air causes lowering of the sealing ability. Also, said leakage of air increases the load of the compressor, which results in a lowering of the entire gas turbine performance.